1. Field of the Invention
The present invention relates to a driving system of a liquid crystal display (LCD) device, and more particularly, to a driving system of an LCD device and an LCD driving method in which an insufficient charging of a liquid crystal capacitor caused by a delayed time taken for raising source and gate signals applied to each pixel of the LCD panel to normal voltage levels is overcome by delaying the source signal generated by a predetermined number of source driver IC units or by delaying the gate signal output by a predetermined number of gate driver IC units.
2. Description of the Related Art
An LCD device is a widely used form of a flat panel display. It takes advantage of light transmittance variations of liquid crystal depending on the voltages applied to each pixel. Especially, the smaller dimension, lighter weight and lower power consumption make an LCD device replace a traditional cathode ray tube (CRT).
LCD devices consist of a liquid crystal panel module, a backlight assembly, and other fixtures. The liquid crystal panel module is a liquid crystal panel with a printed circuit board (PCB) attached. Source driver ICs, gate driver ICs and other components, for example, a controller, are mounted onto the PCB.
A liquid display panel displays an image. Data signals and gate signals are applied to each pixel of the liquid crystal panel. A gate signal is applied to a gate electrode of a thin film transistor (TFT) via a gate line formed in the liquid crystal panel.
The TFT is turned on or off according to a level of the gate voltage. When the TFT is turned on or off according to a gate voltage, the liquid crystal array changes according to the electric field between a pixel electrode and an opposing electrode determined by a voltage level applied to a source electrode. Thus, the liquid crystal capacitor is charged, which varies the degree of light transmittance.
A liquid crystal display displays a certain image according to the above-described method.
Referring to FIG. 1, a gate drive unit 4 having a plurality of gate driver ICs applies gate signals to a liquid crystal panel 2 and a data drive unit 6 having a plurality of source driver ICs applies source signals to a liquid crystal panel 2. Gate drive unit 4 sequentially applies gate signals to the liquid crystal panel 2 vertically in order to turn on and turn off the pixel. Data drive unit 6 sequentially applies source signals to the liquid crystal panel 2 horizontally to charge the liquid crystal. A timing for applying gate voltages and source voltages is set as shown in FIG. 2A.
However, generally, the gate signal is gradually delayed as it goes from position A toward position B of liquid crystal panel 2, and the source signal is delayed as it goes from position A toward position C.
In more detail, as shown in FIG. 2A, the voltages applied for gate signals and source signals are in order at position A of FIG. 1. The gate voltage swings between turn-on voltage Von of 20V and turn-off voltage Voff of xe2x88x92-7V, and the source voltage has a black level which varies in accordance with a positive or a negative polarity.
Voltages of the source signal for each pixel swing between voltage V+ and voltage Vxe2x88x92 for indicating a specific grey level according to the polarity. In FIG. 2, G and S respectively denote the gate voltage and the source voltage. A data signal is applied to a source electrode of TFT as a gray voltage. Hereinafter, data signals and source signals may be used interchangeably.
Source signals and gate signals have timings according to a preset sequence as shown in FIG. 2A. A gate signal rises a certain period after a source signal has risen. The source signal falls down a certain period after the gate signal has fallen. When the source signal maintains the voltage level of V+, the gate signal transits to the turn-on level. Thus, a TFT turns on a pixel and the signal is charged to the liquid crystal capacitor. The source signal charges the liquid crystal capacitor during the time gap Ts, and the lowered gate signal turns off the TFT and pixel during the time gap Tg. These time gaps are adjustable.
Meanwhile, the liquid crystal panel 2 has a resistance and a capacitance due to the gate lines and the data lines. The resistance and the capacitance change the waveforms of source signals and gate signals at each position, as shown in FIG. 2. The waveforms change more as getting away from the terminal where signals are applied. Therefore, as shown in FIGS. 2B and 2D, the waveform of the gate signal changes slowly as getting away from the gate drive unit 4, and as shown in FIGS. 2C and 2D, the waveform of the source signal changes slowly as getting away from the data drive unit 6.
In general, a scanning period of a gate line gets shorter as high resolution and large screen products are developed. When driving a liquid crystal display as shown in FIG. 2, a conventional driving method may not secure a sufficient turn-on time for the pixel. Especially, pixels may be dramatically undercharged when the line resistance and capacitance affect the source signals and the gate signals. This degrades the picture quality and an overall uniformity of display.
As the technology for a high resolution and large screen display develops, a need has risen for a method to secure a sufficient charging time for the liquid crystal capacitor even when a gate line scanning period gets shorter.
It is therefore an object of the present invention to adjust a source signal to be delayed by data line units connected to a source driver IC, considering that it takes longer for gate signals and source signals to rise to the level required for charging the liquid crystal capacitor as getting away from the terminal to which gate signals and source signals are applied. This ensures a turn-on time period of a pixel and enhances a charging rate of a liquid crystal capacitor.
It is another object of the present invention to adjust a gate signal to be delayed by gate line units connected to a gate driver IC, considering that it takes longer for gate signals and source signals to rise to the level required for charging the liquid crystal capacitor as getting away from the terminal to which gate and source signals are applied. It also ensures a turn-on time period of a pixel and enhances a charging rate of a liquid crystal capacitor.
According to one aspect of the present invention, there is provided a driving system of an LCD device including a power supply unit for supplying a direct current voltage, a controller for outputting data and control signals for forming a selected image, a gray voltage generating unit for generating a plurality of gray voltages using a voltage supplied from the power supply unit, a gate voltage generating unit for outputting a gate voltage using the voltage supplied from the power supply unit, a source drive unit for outputting source signals with an input of the data, a portion of the signal contained in the control signals, and the gray voltages, a gate drive unit for outputting gate signals by having other portion of the signal contained in the control signals, and a gate turn-off or turn-on voltage applied thereto, and a liquid crystal panel for displaying the image driven by the gate and source signals applied thereto.
Here, the data drive unit includes a delay part that accepts a load signal and outputs load signals delayed as passing through a first, a second, a third, . . . , and an mth delay units, and n number of source driver ICs that outputs a certain number of source signals according to the control signals (nxe2x89xa7m). Load signals from the delay units are applied to at least one source driver IC that outputs the source signal delayed according to the delay time of the load signal.
The delay part consists of a serially arranged delay units having a resistance and a capacitor arranged in parallel. It delays the load signal. Preferably, the first input load signal and the delayed load signal coming from each delay unit are input to at least one source driver IC. The delay unit corresponds one-to-one to the source driver IC or one-to-many to the source driver ICs.
According to another aspect of the present invention, there is provided a driving system of an LCD device including a power supply unit for supplying a DC voltage, a controller for outputting data and control signals for forming a selected image, a gray voltage generating unit for generating a plurality of gray voltages using the voltage applied from the power supply unit, a gate voltage generating unit for outputting a gate turn-on and turn-off voltage using the voltage applied from the power supply unit, a source drive unit for outputting source signals by having the data, a portion of the signal contained in the control signals, and the gray voltage which are input thereto, a gate drive unit for outputting gate signals by having other portion of the signal contained in the control signals, and the gate turn-on or turn-off voltage are applied thereto, and a liquid crystal panel for displaying the image being driven by the gate and source signal applied thereto.
Here, the gate drive unit includes a delay part that accepts an enable signal and outputs enable signals delayed as passing through a first, a second, a third, . . . , and an xth delay units, and y number of gate driver ICs for outputting a predetermined number of gate signals being driven by the control signals (wherein, yxe2x89xa7x). Enable signals from the delay units are input to at least one gate driver IC that outputs the gate signal delayed according to the delay time of the enable signal.
The delay part consists of a serially arranged delay units having a resistance and a capacitor arranged in parallel. It delays each enable signal. Preferably, the first input enable signal and the delayed enable signals coming from each delay unit are input to at least one gate driver IC. The delay unit may correspond one-to-one to the gate driver IC or one-to-many to the gate driver ICs.
According to the present invention, there is provided a liquid crystal panel driving method in which gate signals and source signals are output to the liquid crystal panel by driving a plurality of gate and source driver ICs in accordance with a data signal for displaying an image, control signals, gray voltages, or a selectively applied gate turn-on or turn-off voltage and operating the liquid crystal panel by said gate and source signals, wherein the gate and the source signals has a sequence of the source signal rising, the gate signal turning on, the gate signal turning off, and the source signal falling, and the source signals are divided into a selected number of source line units, and applied to the liquid crystal panel being accumulatively delayed by a selected time from the time when the gate signal is turned off.
According to the present invention, there is provided a liquid crystal panel driving method, including the steps of outputting gate and source signals to the liquid crystal panel by driving a plurality of gate and source driver ICs in accordance with a data signal for displaying an image, control signals, gray voltages, or a selectively applied gate turn-on or turn-off voltage and operating the liquid crystal panel by a gate and a source signals, wherein the gate and the source signals has a sequence of the source signal rising, the gate signal turning on, the gate signal turning off, and the source signal falling, and the gate signals are divided into a selected number of gate line units, and applied to the liquid crystal panel being accumulatively delayed by a selected time from the time when the source signal is applied.
Here, the gate signal is accumulatively delayed for each gate driver IC and applied to the liquid crystal display. Preferably, the gate driver IC most adjacent to the output terminal of the source signal, from the liquid crystal panel, outputs a gate signal being delayed by total delay time divided by the total number of gate driver lCs after the source signal is output. Subsequently, the other gate driver ICs output gate signals delayed by the total time delay/total number of gate driver ICs.